Program Spotlight

This week precast panels of the SR 99 tunnel’s lower deck are arriving in Seattle. This marks the beginning of an important stage of tunnel construction.

The upper deck of the tunnel’s double-deck highway has been under construction for some time; it was more than half complete by the time the tunneling machine Bertha finished mining in April. The contractor, Seattle Tunnel Partners, is building the upper deck and most of the tunnel’s other interior structures using the … more

In August, we held an open house and online open house to discuss viaduct demolition. We are planning the work, scheduled to begin in full once the SR 99 tunnel opens in early 2019, and we wanted to tell you what lies ahead and ask for your comments and concerns.

Thank you to the 12,000 people who visited our online open house and the 150 people who attended the Aug. 10 open house on Seattle’s waterfront. In total, we received 410 responses to our eight-question survey. We will use … more

Contracts aren’t the highest-profile part of our work to replace the Alaskan Way Viaduct. You can’t see them as you drive on SR 99, they aren’t photogenic, and a contracting time-lapse camera would be one of the dullest things on the internet. But the viaduct demolition contract we’re awarding early next year will have a big effect on your experience traveling through downtown Seattle.

The new SR 99 tunnel, currently scheduled to open to traffic in … more

When Bertha finished digging on April 4, 2017, it marked the end of one critical element in the work of building the new SR 99 tunnel. It also marked the end of a straightforward, if simplified, way to track progress on building the tunnel (distance tunneled).

With Bertha’s disassembly nearly complete, we are shifting our focus to the other elements of work remaining before the tunnel is ready for traffic. This week we debut a new way to track this progress.

Milepost 31 in Pioneer Square is gearing up for a busy summer of programming. Our information center continues to offer free public viewing platform tours to see the SR 99 tunnel’s south portal construction site. Bike tours have also resumed, which follow Bertha’s tunnel route and provide a unique way of understanding the historical and engineering aspects of this megaproject. You can sign up for tours online or in person at the center.

Bertha, the SR 99 tunneling machine, has completed her 9,270-foot journey beneath Seattle. Although tunnel boring has come to end, crews have significant work to do before the tunnel can open to traffic in 2019.

Construction of the SR 99 tunnel can be broken down into five activities:

Clean air is a critical element of a safe and well-functioning tunnel. In the new SR 99 tunnel, a complex system of fans will push and pull air into and out of the tunnel to ensure fresh air during routine operations and in emergencies.

The first element of the tunnel’s ventilation system is the very traffic that uses it. Vehicles traveling through the tunnel will act like pistons, pushing fresh air into the tunnel. But when that piston effect needs a boost, the tunnel will turn to … more

When the SR 99 tunnel opens to traffic, drivers on northbound SR 99 will use a new off-ramp near the stadiums to reach downtown Seattle. In addition to linking travelers to their destination, engineers and researchers hope the new ramp will provide a link to something else: earthquake-resistant bridges.

By combining memory-retaining metal rods and a bendable concrete composite, the future off-ramp will become the first bridge in the world built to sway with a strong earthquake and … more

Performing regular maintenance on Bertha, the SR 99 tunneling machine, is critical to the success of the tunnel drive. During each of Seattle Tunnel Partners’ three planned maintenance stops in 2016, crews have spent time checking and maintaining various systems throughout the machine. Specific maintenance needs vary with each stop, but one maintenance item is always on STP’s to-do list: inspection and replacement of cutterhead tools.